Multi-parameter inspection apparatus for monitoring of additive manufacturing parts

ABSTRACT

Additive manufacturing, such as laser sintering or melting of additive layers, can produce parts rapidly at small volume and in a factory setting. To ensure the additive manufactured parts are of high quality, a real-time non-destructive evaluation (NDE) technique is required to detect defects while they are being manufactured. The present invention describes an in-situ (real-time) inspection unit that can be added to an existing additive manufacturing (AM) tool, such as an FDM (fused deposition modeling) machine, or a direct metal laser sintering (DMLS) machine, providing real-time information about the part quality, and detecting flaws as they occur. The information provided by this unit is used to a) qualify the part as it is being made, and b) to provide feedback to the AM tool for correction, or to stop the process if the part will not meet the quality, thus saving time, energy and reduce material loss.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional patent application of U.S. patentapplication Ser. No. 16/595,390, filed on Oct. 7, 2019, which is acontinuation-in-part of U.S. Provisional Patent Application No.62/742,807, filed on Oct. 8, 2018 and U.S. Provisional PatentApplication No. 62/771,568, filed on Nov. 26, 2018, the disclosures ofwhich are hereby incorporated by reference in their entirety to providecontinuity of disclosure to the extent such disclosures are notinconsistent with the disclosure herein.

BACKGROUND

Additive manufacturing, such as laser sintering or melting of additivelayers, can produce parts rapidly at small volume and in a factorysetting. Ensuring production quality is crucial for additive (AM)manufacturing. To ensure the parts are of high quality, a real-timenon-destructive evaluation (NDE) technique is required to detect defectswhile they are being manufactured. The present invention describes anin-situ (real-time) inspection unit that can be added to an existingadditive manufacturing (AM) tool, such as an FDM (fused depositionmodeling) machine, or a direct metal laser sintering (DMLS) machine,providing real-time information about the part quality, and detectingflaws as they occur. The information provided by this unit is used to a)qualify the part as it is being made, and b) to provide feedback to theAM tool for correction, or to stop the process if the part will not meetthe quality, thus saving time, energy and reduce material loss. Thedescribed NDE technique is incorporated in additive manufacturingmachine to capture defects in real time or any other metal printingtool. The sensor data is used to identify defects as they occur suchthat real-time corrective action can be taken. It also providesparameters that enable the prediction of the part quality

SUMMARY

The present invention describes a real-time (in-situ) non-destructiveinspection (NDI) that uses a combination of multiple sensing/imagingmodalities for detecting defects in additive manufacturing (AM) parts,such as 3D printed parts. These include multi-angle imaging, scanningradial illumination imaging, and polarization imaging, speckleillumination imaging, modulated speckle illumination imaging,multi-wavelength imaging, and spectral and temporal imaging to determinecooling rate. The final outputs are combined to produce a defect map.Each of these techniques detects different types of defects as describedin the Technical Approach section. For example, scanning radialillumination reveals out-of-spec angled print layers, or gaps betweenprint lines. Polarization imaging reveals variations in print layerfinish, and can be used for measuring stress in optically clearplastics. Modulated speckle illumination measures micro-pits, voids,discontinuities, and multi-wavelength imaging is used for multi-materialassessment to distinguish between defects at different material prints.In addition, it can be used in conjunction with polarization detectionfor birefringence measurements, such as for measuring stress in the partbeing printed. The multi-angle image reveals out-of-spec angled 3Dprints. The speckle illumination approach measures granularity andsurface roughness to detect micro-voids and non-fused metal. Spectraland temporal measurements detect of variations in cooling rates toreveal voids and discontinuities. An overview of the NDI approach isshown in FIG. 1 .

Using multi-parameter detection enables a robust real-time inspectionmethod that provides measurement redundancy, maximizing likelihood ofdetecting defects that may otherwise be missed using a single parametersensing approach, and avoids false readings. This method provides fastand high spatial resolution defect detection to enable both partqualification after the print is completed, without requiring postinspection, as well as providing information to enable correctiveaction, such as to stop a potentially defective print, or to makereal-time correction and continue the additive manufacturing process.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention relating to both structure and method ofoperation may best be understood by referring to the followingdescription and accompanying drawings.

FIG. 1 is a perspective pictorial and block diagram illustratingoverview of detecting defects in additive manufacturing parts.

FIG. 2 is a perspective pictorial and block diagram illustrating anembodiment for detecting defects in additive manufacturing parts.

FIG. 3 is a perspective pictorial and block diagram illustrating anotherembodiment for detecting defects in additive manufacturing parts.

FIGS. 4A and 4B are pictorial diagrams showing images and dataillustrating an example of images and data obtained using angularscanning illumination to reveal defects in metal prints.

FIGS. 5A to 5C are perspective pictorial and block diagrams illustratingan embodiment that describe angular scanning illumination.

FIGS. 6A to 6C are examples of results of speckle-controlledillumination tests.

FIGS. 7A and 7B show two types of apparatus to generate coherentillumination. FIGS. 7C and 7D are perspective pictorial and blockdiagrams illustrating an embodiment for modulated speckle illumination.

FIG. 8A shows spectral emission of hot metal calculated from blackbodyradiation model.

FIG. 8B shows relative emission at 650 and 940 nm versus temperature.

FIG. 9 is a perspective pictorial and block diagram illustrating anembodiment for mufti-wavelength imaging.

FIG. 10 illustrates use of a combination of cameras and narrowbandoptical filters to capture an image of the hot surface.

FIGS. 11A and 11B show an example of image improvement using specklenoise reduction techniques.

FIG. 12 is a perspective pictorial and block diagram illustrating anembodiment for polarization imaging.

FIGS. 13A to 13F are perspective pictorial and block diagramsillustrating various multi-state polarization detection methods.

FIG. 14 is a perspective pictorial and block diagram illustrating amulti-wavelength polarization imaging.

FIGS. 15A to 15F are pictorial diagrams showing images and data obtainedusing angular scanning illumination.

FIGS. 16A and 16B are pictorial diagrams showing images and dataobtained using polarization imaging.

FIGS. 17A and 17B are pictorial diagrams showing images and dataobtained using polarization imaging and spectral filtering forbirefringence and stress detection.

FIGS. 18A and 18B are pictorial diagrams showing images and dataillustrating an example of images and data obtained using modulatedspeckle illumination.

FIGS. 19A to 19C are pictorial diagrams showing images and dataillustrating an example of images and data obtained using angularscanning illumination to reveal incorrect print angles or print anglevariations.

DETAILED DESCRIPTION

FIG. 1 is a pictorial block diagram illustrating a schematic of areal-time inspection unit for detecting defects in additivemanufacturing parts during printing using a multi-modal inspection 100.Multi-modal inspection apparatus 101 is comprised of light sources,components and detectors described herein is connected to an additivemanufacturing unit, such as a 3D printer, either mounted internally, orexternally, such as through a viewing window or an opening port, or acombination thereof. The apparatus is controlled by a set ofelectronics, namely a control unit 102. Sensor outputs 103 send signaland image data for processing that indicate various parameters about theprinted part, such as presence of defects, and deviation from theoriginal part design. The outputs are either pre-processed 104digitally, or the raw sensor data is used, each corresponding to variousinspection modalities 105. Inspection modalities 105 are combined toproduce a defect map and to determine part quality 107 eitherindividually or by combining with other modalities 106. These modalitiesinclude multi-angle imaging, scanning radial illumination imaging, andpolarization imaging, speckle illumination imaging, modulated speckleillumination imaging, multi-wavelength imaging, and spectral andtemporal imaging, or a combination thereof. The information from thedefect map 107 is used to a) determine part quality, b) stop the print,if the part is deemed too defective, or c) as a printer feedback 108 tomake corrective action to the part being printed by modifying thesubsequent print layers to correct for the detected defects.

Using multi-parameter detection enables a robust real-time inspectionmethod that ensures printed part quality. It provides measurementredundancy, maximizing likelihood of detecting defects that mayotherwise be missed using a single parameter sensing approach, andavoids false readings. In some embodiments, the apparatus depictedherein are used for quality control and used as an add-on unit forquality control and feedback to additive manufacturing (AM) toolavailable in the market.

The advantage of the use of multi-parameter approach is that eachparameter reveals various types of defects, thus it covers a broad rangeof print quality and additive manufacturing issues in a compact,light-weight, and high sensitivity robust manner.

Multi-Angle Sensing

FIG. 2 depicts sintering laser entrance windows 201, wherein a sinteredlaser beam is capable of entering through the window and interactingwith the metal part 206 to be sintered, a controlled speckle generationsource 202, multi-wavelength LEDs 203, cameras 204 with optical filters215, timing signals 205, metal part 206, pre-processing 207 such asspatial filtering, temporal filtering between frames image frames,low-pass or high pass filtering, Fourier filtering and Fourier analysis,Fourier transforms, differentiation, multiple frame addition,subtraction, multiplication, background subtraction, morphological imageprocessing, wavelet transforms, and thresholding, powder beds 208,multi-angle data 209, speckle data 210, multi-wavelength, data andcooling time 211, combined defect map and decision 212, printer feedback213, and incident angles 214. Multi-angle data 209 provide informationabout the presence of surface defects, such as voids anddiscontinuities. Speckle data 210 produces information about smalldefects, and multi-wavelength data and temporal measurements betweenmultiple frames which produce cooling time 211 in each area of thespecimen which indicates presence of surface and subsurface defects. Thepre-processing 207 of the raw data, combined with the multi-angle data209, speckle data 210, and cooling time data 211 are combined, namely byimage or data addition, thresholding, and spatial filtering the outputsof each of these to produce a defect map 212. The defect map 212 showsposition and size of surface and subsurface defects. This information isused a) to produce the quality of the part at each print layer, b) todetermine if the part passes a certain threshold and that if the ifprint can continue, and c) and to send corrective information to the AMtool such that print layer information can be modified to correct fordefects. This information is used as a printer feedback 213 so thatsubsequent layers can be corrected. For example, if a void is detectedand the subsequent print will fill in that void by extra material.

FIG. 2 illustrates distributed light sources, such as light emittingdiodes (LED) 203, positioned such that each produce a differentillumination angle of incidence. The cameras across from the lightsource, as well as the cameras 204 placed on all side capture thereflected image from the printed portion of the part in the powder bed208. Each light source 203 covers a narrow range of angles, and acombination of multiple light sources produce a full range of angularmeasurements as shown in FIG. 2 . The light sources 203 are rapidlysequenced to produce multi-angle images 209 captured by the cameras.Light sources are rapidly sequenced by applying a signal such as 205,namely by changing the electrical current or voltage applied to eachlight source to turn it on or off, or to reduce the light source'sluminous output. The signal to sequence the light source is applied byan electrical circuit, which is synchronized to the image capture of thecameras. FIG. 2 also includes speckle generation sources 202.

In some embodiment this apparatus is use for in-situ detection, such asfor detection while the material is being printed using the additivemanufacture apparatus. In other instances, the apparatus is used fordetection of detects after the parts are manufactured, such as forprinted part inspection, verification and qualification.

FIG. 3 is an overview of in-situ technology incorporated inside additivemanufacturing unit. Multiple parameters are measured, namely using i)Scanning angular or radial illumination by sequentially turning on orpulsing each light source and detecting each angle ii) polarizationimaging using polarization components that are mounted in front of thecameras, or using multiple adjacent cameras with polarizers orientedorthogonal to each other (this is not shown to avoid crowding of thefigure). iii) Modulated speckle illumination generated by a combinationof laser diodes, and scattering media, to detect very small defects, andiv) multi-wavelength imaging, where a combination of multi-wavelengthLED-s are used for identifying defects in each specific material printsection in a multi-material part manufacturing. Additionally, acombination of polarization and multi-wavelength measurements can yieldstress in an optically clear part being printed by measuringbirefringence.

FIG. 3 depicts a print head 301, speckle generation source 302,multi-wavelength LEDs 303, cameras with optics and polarizers 304,timing signals 305, part being printed 306, pre-processing 307, 3D printmodel (e.g., STL the) 308, expected parameters, scanning radialillumination data 309, differential speckle correlation data 310,polarization data 311, multi-wavelength data 312, stress data 313,combined defect map part quality indicator 314, and printer feedback315. Pre-processing 307 are digital operations such as spatialfiltering, temporal filtering between frames image frames, low-pass orhigh pass filtering, Fourier filtering and Fourier analysis, Fouriertransforms, differentiation, multiple frame addition, subtraction,multiplication, background subtraction, morphological image processing,wavelet transforms, and thresholding. Scanning radial illumination data309 provides information about the presence of surface defects, such asvoids and discontinuities. Differential speckle correlation data 310provides information about small defects. Polarization data 311 producesinformation about presence of defects such as small prints that deviatefrom an original intended print angle. Multi-wavelength data 312provides information about defects that are of different material, ifusing different type of prints. In addition, when multi-wavelength data312 is combined with polarization data 311, they produce informationabout birefringence and stress 313, as described throughout the presentinvention and in equation 3, such as for detecting stress builds in atransparent or translucent type print. All this information is combined,such by image or data addition, thresholding, and spatial filtering theoutputs of each of these, to produce a defect map and part qualityindicator 314. The defect map 314 shows position and size of surface andsubsurface defects. This information is used a) to produce the qualityof the part at each print layer, b) to determine if the part passes acertain threshold and that if the if print can continue, and c) to sendcorrective information to the AM tool such that print layer informationcan be modified to correct for defects. This information is used as aprinter feedback 315 so that subsequent layers can be corrected. Forexample, if a void is detected and the subsequent print will fill inthat void by extra material.

FIGS. 2 and 3 illustrate light sources such as light emitting diodes(LED) 203 and 303, positioned such they produce illumination atdifferent angles of incidence. The cameras are placed across from thelight source, as well as the cameras placed on various sides of theprint chamber capture the reflected image from the printed portion ofthe part. Each light source covers a narrow range of radial angles, anda combination of multiple sources produce a full range of angularmeasurements as shown in FIG. 2 and FIG. 3 . The light sources arerapidly sequenced to produce multi-radial scan images captured by thecameras. Light sources are rapidly sequenced by applying a signal suchas 205 and 305, namely by changing the electrical current or voltageapplied to each light source to turn it on or off, or to reduce thelight source's luminous output. The signal to sequence the light sourceis applied by an electrical circuit, which is synchronized to the imagecapture of the cameras.

It is to be understood that defects such as voids, missing lines, largegaps, bulging material, improperly fused material and areas withincorrect print angles have different radial angular reflectioncharacteristics than surrounding correctly printed areas. Therefore, aunique aspect of the present invention is that the scanning angularillumination measurements of the present invention reveal these defects.For example, a smooth surface produces angle of reflection θ_(r), thatis equal to angle of incidence, θ₁. namely θ_(i)=θ_(r). Localdifferences in printed surface angles appear as brightness variations inthe image. Additionally, non-smooth surfaces producereflection/scattering at wider range of angles.

Another example is when there is a large gap in some of the lines thatare too fine to be viewed and distinguished by standard imaging. Thearea with the gap causes light to go through the gap and reflect fromthe previously printed layer. Note however in order to detect thesegaps, an angular scan is necessary, because only certain angles ofincident will reveal the defect. It should be noted that the reflectedimage for each angle (I_(r)) illuminated image, I_(R)(x,y,θ_(r)),reveals the directionality of the defect with respect to theillumination angle, and provides critical knowledge of the defectlocation and orientation. For a quality assurance however, and overalldefect map can be obtained, I_(RTot)(x,y), by an integral all theangular scans, namely:I _(R) _(Tot) (x,y)=∫(x,y,θ _(r))dθ _(r)  (Eq. 1)

Other information that can be extracted from these measurements is tomeasure variations between multiple images of different illuminationangles. Digitally, this is achieved using one of several digitalprocessing techniques, such as comparing normalized difference between 2or more images, performing correlation or convolution in the spatialdomain, or multiplication in the Fourier domain.

In some embodiments, the angular scan depicted in FIGS. 2 and 3 revealsincorrect print angles or print angle variations.

In some embodiments, this apparatus is used for in-situ detection, suchas for detection while the material is being printed using the additivemanufacture apparatus. In other instances, the apparatus is used fordetection of detects after the parts are manufactures, such as forprinted part inspection, verification and qualification.

In some embodiments, the light source and the camera are at fixedpositions. In other embodiments, the light source or the camera, or bothare shifted mechanically. Yet in other embodiments, multiple lightsource, multiple cameras, or a combination of both are placed at variousangular positions, and when the light source is turned on simultaneouslyor sequentially, cameras capture is turned on simultaneously orsequentially, or a combination thereof. Yet in other embodiments, thevarious light source and camera turn on time and capture time aresynchronized to produce images and detection data at various detectionangles.

Since reflection between multiple layers has different angularcharacteristics, such as different angles of scattering, and differentreflections, defects such as voids, line breakage and missing lines orlarge gaps in the lines can be detected using angular scanningillumination.

In sensor arrangements described throughout the present invention anddepicted in FIGS. 2, 3 and 5 , angular scan refer to scan in the radialdirection, namely in the x-y direction depicted in FIG. 5B, or scan inthe vertical direction, namely in the x-z direction depicted in FIG. 5C,or a combination of both, referring to any arbitrary angle in the x, y,and z directions.

The terms angular and radial are used interchangeably throughout thisapplication.

FIGS. 5A to 5C are perspective pictorial and block diagrams illustratingan embodiment that describes angular scanning illumination. FIG. 5Adepicts a perspective a light source 501 that is moving at variousangular positions with respect to camera 502, thereby detecting defectsas they occur while the specimen is being printed, or after the print iscomplete. FIG. 5B is the top view indicating the variation in the anglesin radial direction, and FIG. 5C is the side view of the detection,indicating variations in the vertical angular direction 507. FIG. 5depicts light source 501, camera 502, 3D printed specimen 503, incidentangle in planar x-y direction 504, reflected or scattered angle inplanar x-y direction 505, incident angle in vertical x-z direction 506,and reflected or scattered angle in vertical x-z direction 507.

In some embodiments, the light source 501 and the camera 502 are atfixed positions. In other embodiments, the light source or the camera,or both are shifted mechanically. Yet in other embodiments multiplelight sources, multiple cameras, or a combination of both are placed atvarious angular positions, and when the light source is turned onsimultaneously or sequentially, the cameras capture is turned onsimultaneously or sequentially, or a combination thereof. Yet in otherembodiments, the various light source and camera turn on time andcapture time are synchronized to produce images and detection data atvarious detection angles.

Since reflection between multiple layers has different angularcharacteristics, such as different angles of scattering, and differentreflections, defects such as voids, breakage, bulging and missing linesor large gaps in the lines can be detected using angular scanningillumination.

The terms angular and radial are used interchangeably throughout thisapplication.

Defects such as voids, edges near missing lines, bulging material,improperly fused metal and areas with incorrect print angles havedifferent angular reflection characteristics than surrounding correctlyprinted areas. Therefore, the angular measurements of the presentinvention reveal these defects. For example, a smooth metallic surfaceproduces angle of reflection θ_(r), that is equal to angle of incidence,θ_(i). Namely θ_(i)=θ_(r). Local differences in printed surface anglesresult in variations in the image. Additionally, non-smooth surfacesproduce reflection/scattering at wider range of angles. Thesedifferences can also be detected with angular measurements.

For example, a stainless-steel sample printed by direct metal lasersintering (DMLS) are tested for surface quality by imaging usingdifferent angles of illumination. The tests reveal a few spots that weredifferent than the rest of the print area. These defects are verified bymicroscope inspection. The results are shown in FIG. 4 . Using twoangles of illumination, for example at 30 and 57 degrees, defectivespots of two different surface angles are revealed.

FIGS. 4 and 4B illustrate measuring surface quality by changing sourceangle, such as on a DMLS printed steel stainless sample. The lightsource (not shown) is set at 30-degree incidence in FIG. 4A, and 57degree in FIG. 4B. The camera (not shown) is at a fixed position. Theimage width is approximately 60 mm. This example illustrates a detectionof defects 402 on a printed part as outlined 401. Each measurement atdifferent angles reveals a different set of defects 402.

In some embodiments, the sensor unit described herein is incorporated inthe 3D printing machines without requiring design changes to themachine. The unit will detect printing defects in real-time. In otherembodiments, the sensor data is utilized to pre-qualify parts forquality, and therefore minimize or eliminate the need for postfabrication testing.

Detection of Defects Using Speckle Illumination

Speckle noise is often a nuisance in coherent imaging applications. Inthe technique described in the present invention however, coherentillumination is utilized to detect very small variations in print lines,such as voids and pits. Because of its coherence characteristics, laserillumination results in speckle pattern when it passes through a diffusemedia. Speckle size dependents on the random distribution of the diffusemedia, and aperture size or the illumination spot incident on thediffuse media. When this diffuse illumination pattern is incident on aprint surface with areas that contain pits, voids, or small defects onthe order of the speckle size, a very bright signal is detected by thecamera viewing the illuminated part. Therefore, small defects can bedetected by this approach which is a unique aspect of the presentinvention. Another method of generating a speckle illumination is usinga mufti-mode fiber. The two methods of generating speckle pattern areshown in FIGS. 7A to 7D, as will be discussed in greater detail later.

The observed image however will be very noisy, which is a characteristicof coherent illumination. To reduce speckle noise from the image whilemaintaining the advantage of coherent detection, either the randommedia, or the multi-mode fiber shown in FIGS. 7A to 7D are moved tosmooth the detected image, as will be discussed in greater detail later.

To ensure that the signal is due to pits or other small defects, and tominimize chance of false calling a defect, the speckle generation sourceis spatially modulated as shown in FIGS. 7A to 7D, as will be discussedin greater detail later. Dust and other sources of noise can cause abright spot in the image, as well. Pits and other stationary defectsresult in a bright spot in the image which re-appear as the specklegeneration source is moved, or spatially modulated, whereas randomspeckle noise is a one-time occurrence. Therefore, spatial modulationwill enable elimination of false readings. This approach can easilydistinguish between a signal due to actual defects in the print and asignal due to dust and other particles, because the signal from defectsis relatively stationary with respect to the sample.

In another embodiment similar to FIGS. 7A to 7D, multiple coherent orpartially coherent light sources of the same or different wavelengthsare used to enable testing of materials of different characteristics andreflectivity.

Yet in other embodiments similar to FIG. 7A, speckle size is fixed,varied, or controlled to detect various size defects by controlling theillumination spot size on the diffuse media, or by selection of diffusemedia granularity, or a combination thereof.

Yet in other embodiments similar to FIG. 7B, speckle size is fixed,varied, or controlled to detect various size defects by controllingoptical fiber shape, size of the granularity, or polishing grit off thetip, the tapering angle, or a combination thereof.

Coherent illumination will generate an image that is full of specklenoise which makes it difficult to separate the signal from the defectivearea from noise. To overcome this, speckle noise reduction is achievedby rapidly moving the diffuser or the speckle generating fiber. Itshould be noted that even though the speckle pattern is moving, it willstill reveal the defects, but noise in the image will be significantlyreduced.

FIG. 11 an example of speckle noise reduction 1100 while imaging aspecimen 1101, and speckle noise 1102. When the fiber or diffuserdepicted in FIGS. 7A to 7D is stationary, the image produced is verynoisy as indicated in FIG. 11A. When the diffuser or multi-mode fiberare moving rapidly, the speckle noise is minimized or removed, and thespecimen 1101 or the part being printed is imaged with clarity, asdepicted in FIG. 11B.

Speckle noise is often a nuisance in coherent imaging applications. Herehowever advantage is taken of coherent illumination by controllingspeckle sizes to determine the granularity of the printed surface, andfinding improperly fused material. Because of its coherencecharacteristics, laser illumination results in a speckle pattern whenthe laser passes through a diffuse media. Speckle size depends on therandom distribution of the diffuse media and aperture size or theillumination spot on the diffuse media. When laser light scattered by adiffuser illuminates a medium of a specific granularity, such as a 3Dprinted metal surface, the scattered light is proportional to spatialcorrelation of the speckle distribution of the incident illumination andthe spatial distribution of the granular media. Therefore, grain sizeand distribution characteristics of the metal surface can be obtained bycontrolling the speckle size of the illumination spot on the diffusemedia. Therefore, the image intensity distribution captured by thecamera shown in FIG. 2 will depend on speckle size and granularitydistribution of the printed surface.

Speckle size-controlled imaging demonstrates this effect as depicted inFIGS. 6A to 6C. Areas or spots of different granularity on a metal partprinted by direct metal laser sintering (DMLS) are detected using threedifferent speckle size illuminations. This is achieved by controllingspeckle size from coarse (FIG. 6A) to medium (FIG. 6B) to fine (FIG.6C). The 3D printed stainless steel part is outlined in the dotted line601. Defects 602 of different granularity are detected by controllingspeckle size from coarse (FIG. 6A) to medium (FIG. 6B) to fine (FIG.6C). Speckle size is controlled by controlling illumination areaaperture on a moving diffuser. FIGS. 6A to 6C image widths are 25 mm.

Current 3D metal printers, such as DMLS, use high power lasers to meltthe material directly without the need for post processing. If there isimproper melting, there will be voids and discontinuities in the printedsurface. The granularity of improperly fused section will be different(there will be many micro voids present), and this will be detectedusing the speckle imaging method.

FIGS. 7A to 7D show various methods of generating illumination ofdifferent speckle sizes. In FIG. 7A, a diffuse media combined withaperture control generates speckles of a desired size. In FIG. 7B,multi-mode fibers of different diameters (or using fiber tapers) areused to generate speckles of different size.

FIGS. 7A to 7D show two types of apparatus to generate coherentillumination 701 for granularity measurements. Speckle size 705 iscontrolled using aperture control and diffuse media (FIG. 7A), and usinga multi-mode fiber of different sizes (FIG. 7B). To remove speckle noisefrom the image, the random media or the multi-mode fiber can be movedduring image acquisition. FIGS. 7A, 7B depict a coherent light source701, a moving diffuser 702, and optics and iris 703, and controlledaperture 704. The apparatus controls the speckle size 705, andincorporates a moving fiber 706 that reduces the speckle noise in thedetected image.

In the apparatus shown in FIGS. 7A to 7D, several coherent sources areused (such as laser diodes) in conjunction with speckle generationapparatus. Each source generates a particular range of sizes ofspeckles. The source is combined either with optics and random media asshown in FIG. 7A, or coupled to multi-mode fibers of different aperturesas shown in FIG. 7B. When using multi-mode optical fibers, either fibersof different diameters are employed, or aperture is controlled usingfiber tapers. An example of fiber tapers are illustrated in FIG. 7A.

FIGS. 7C and 7D show two types of apparatus to generate coherentillumination for small defect detection. Speckles are generated usingdiffuse media (FIG. 7C), and using a multi-mode fiber (FIG. 7D). Toremove speckle noise from the image, the diffuse media or the multi-modefiber is moved rapidly. To minimize false detection, the specklegeneration apparatus is spatially modulated as described in the herein.FIGS. 7C and 7D depict optics and iris 703, fast moving fiber 706, laserdiode (LD) 708, fast moving diffuser 709, illuminated spot of light onthe diffuser 710 by LD, spatially modulated speckle generator 711, andspeckle illumination 712.

To remove speckle noise from the image, the random media or themulti-mode fiber is moved during image acquisition.

In some embodiments similar to FIGS. 7A to 7D, the coherent source, is alaser diode, a super luminescent source, a light emitting diode (LED), alight source or an LED with a narrow band wavelength filter placed infront of it or in the optical path, a gas laser, a solid state laser, orany other coherent or partially coherent source.

To reduce speckle noise from the image while maintaining the advantageof granularity detection, either the random media, or the multi-modefiber shown in FIGS. 7A to 7D are conventionally moved to smooth thedetected image. Examples of speckle noise reduction are shown in FIG. 11.

FIGS. 11A and 11B are examples of image improvement using specklereduction techniques by moving a diffuser or moving a multimode fiber asdepicted in S 7A to 7D. FIG. 11A shows a surface image of a specimen1101, with image obscured by speckle noise 1102. FIG. 11B shows an imageof the same specimen with speckle noise removed.

Spectral and Temporal Measurement to Determine Cooling Rate

Detecting the rate at which the material cools is a method for detectingdefects. For example, at the presence of voids or discontinuities, theadditive manufactured material cools much slower than an area withoutvoids. The cooling rate can be determined by measuring the spectralemission of metal as it is exposure to the sintering laser, andimmediately after exposure. The emission spectra can be estimated byblackbody radiation model, namely:I(λ,T)=(2hc ²/λ⁵)[exp(hc/λkT)−1]⁻¹  (Eq. 2)

Where h is the Planck constant, c is the speed of light in vacuum, k isthe Boltzmann constant, T is the temperature and □ is the wavelength 802(FIG. 8 ). The emission 801 spectrum for a metal surface that is coolingfrom 1400 deg. C. 804 to 800 deg. C. 805 is shown in FIG. 8A. Monitoringthe output at a single wavelength or at two or more wavelengths in thevisible and near IR spectral range, such as 650 nm 806 and 940 nm 807(FIG. 8B)—wavelengths that are within the spectral detection range ofCMOS cameras, the cooling rate can be calculated. The relative emission801 for these two wavelengths with respect to temperature 803 are shownin FIG. 8B. FIG. 8A depicts the spectral emission of hot metalcalculated from blackbody radiation model. FIG. 8B depicts the relativeemission at 650 and 940 nm versus temperature.

FIG. 8A shows spectral emission of hot metal calculated from blackbodyradiation model. It shows relative emission 801 with respect towavelength 802 for a metal surface that is cooling from 1400 deg. C. 804to 800 deg. C. 805 at 100 degree increments. FIG. 8B shows relativeemission 801 with respect to temperature 803 for two wavelengths, 650 nm806 and 940 nm 805.

Multi-wavelength measurements are achieved using multi-color LED-scombined with monochrome cameras, or using white light sources combinedwith color filters as depicted in FIG. 9 . FIG. 9 depicts light source901, camera 902, filter 1 903, filter 2 904, and specimen 906.

For the apparatus depicted in various figures in the present invention,it is to be understood that the camera image is digitized, transferredto a computer and image processing and computing are conventionallyperformed.

One of the challenges with this kind of imaging is sparking that occursduring powder bed metal sintering. To overcome this, the image isdigitally filtered and processed to remove the sparking noise. Thesparks in the image have characteristic linear shape. Therefore, spatialfiltering of the image by means of Fourier Transformation, and removingthe high-spatial frequency components from the image will remove thisnoise. Details of cooling rate measurement apparatus is shown in FIG. 10which illustrates where a combination of camera(s) and narrowbandoptical filters are used to capture an image of the hot surface. Thesignal amplitude captured by the camera will decay as that section coolsdown, and the rate at which the amplitude decays indicates the coolingrate.

FIG. 10 illustrates cooling-rate measurement 1000 by imaging the hotmetal as it cools down, right after exposure to sintering laser. Narrowpass-band optical filters help increase sensitivity by passing narrowportion of the emission spectrum. Digital filtering reduces the sparknoise. FIG. 10 depicts detection of cooling rate of melting or sinteringspot 1001, sparks 1002 that appear when a sintering laser is incident onmetal powder during 3D metal printing, optical filters 1003,multi-wavelength (visible/IR) cameras 1004, digital filtering 1005 ofthe detected data or image to remove noise in the image, such as noisedue to sparks, change of signal 1009 versus time at each pixel of thecamera at one or more wavelengths such as λ₁ 1006, λ₂ 1007, which resultin determining the cooling rate 1008 of the metal at each spot on theprinted part, extracted from a change in signal at each camera pixel.This is due to the fact that the emission spectra 1010 changes in thetime, namely as the part cools, also depicted in FIGS. 8A and 8B.Changes in the cooling rate are due to the features of the part as wellas due to voids, improperly melted section on the part and other typesof defects. Therefore, cooling rate detection determines the integrityof the part and reveals defects.

During metal 3D printing, areas with defects such as voids cool muchslower than the area without voids. This can also be detected by thedescribed multi-wavelength approach using visible/near IR camera, namelyby rapidly detecting the color change due to cooling right after thesintering or melting laser is turned off or moved to another spot.

FIG. 12 is a perspective pictorial and block diagram illustrating anembodiment for polarization imaging using a light source 1201illuminating a specimen 1204, and a camera 1203 with a polarizer 1202placed in front of the camera. In alternative embodiments, the lightsource can be polarized, randomly polarized or circularly polarized. Inother embodiments, a polarizer, a wave plate or a combination of bothare used in front of the light source to control the state of theincident light polarization.

FIGS. 13A to 13F are perspective pictorial and block diagramsillustrating an embodiment depicting various methods of simultaneouslydetecting multiple polarization states. FIGS. 13A to 13F depict beamsplitter 1301, polarizer 1302, camera 1303, polarization 1304, imaginglens 1305, lens or lenslet array 1306, polarizer array 1307, focal planearray 1308, multiple images each for different polarization state 1309,polarizer fine array 1310, and each pixel or cluster of pixels representdifferent polarization state 1311.

FIG. 13A depicts using a beam splitter 1301, such as a reflective platebeam splitter, a cube beam splitter or a diffractive beam splitter,combined with polarizers in front each camera. FIG. 13B depicts using apolarization beam splitter. FIGS. 13C to 13E illustrates use of lensarray and polarizer arrays to capture multiple polarization states. FIG.13F illustrates use of fine polarizer array in front of the camera, orembedded on the camera chip to produce multiple state polarizationimages. In an alternative embodiment similar to FIGS. 13A and 13B,focusing lenses are placed in front of each camera after the beamsplitter. Yet in another embodiment similar to FIGS. 13A and 13B, afocusing lens is placed before the beam splitter resulting in focusedimages on both cameras. In various embodiments similar to FIGS. 13A to13F, the images are combined digitally to determine various polarizationstates, indicate the difference in between states, and shift the imagesfor overlap of the images, or a combination thereof.

FIG. 14 is a perspective pictorial and block diagram illustratingspectral or multi-wavelength polarization imaging using a combination ofpolarizers, wave-plates and spectral filters. In some embodiments, onlylinear polarizers are used in front of the camera. In other embodiments,polarizers are used in front of the light source and in front of thecamera. Yet in other embodiments, wave-plates are added to control thepolarization state, form linear to elliptical to circular. FIG. 14depicts light source 1401, camera 1402, polarizer, wave plate and filter1403 placed in the incident light path, and a polarizer, wave plate andfilter 1404 placed in the reflected or scattered light path from thespecimen 1406, at an incident angle θ 405.

In some embodiments similar to FIGS. 9 and 14 , a monochromatic light, alaser, a white light, a broad spectral light with a spectral filter infront of it, a spectral are used. In other embodiments, a filter infront of the camera, or a color camera, or a combination thereof areused.

FIGS. 15A to 15F are pictorial diagrams showing images and data obtainedusing scanning radial illumination imaging examples. FIGS. 15A to 15Fdepict part outline 1501, detected defects 1502, and large gap betweenprint lines 1503. FIG. 15A and FIG. 15B show detection with Illuminationat 160 degrees and at 170 degrees, respectively. FIG. 15C and FIG. 15Dare the processed image to remove background of the images in FIGS. 15Aand 15B. FIG. 15E is the digitally combined image of FIG. 15C and FIG.15D as described in equation 1. FIG. 15F is a microscopic inspectionimage of the printed part. Arrows indicate a large gap between the printlines. Data in FIG. 15E matches the gaps observed by the microscopicimage shown in FIG. 15F. Image widths of FIGS. 15A to 15D image are 30mm. Image width of FIG. 15F is 18 mm.

FIG. 16A is a pictorial diagram showing an image of a 3D printedspecimen 1601 viewed with standard room light illuminated. FIG. 16B is apictorial diagram showing the specimen being imaged through a verticalpolarizer which indicates two spots (inside the dotted circle) that havedifferent print angles than the other surrounding area. FIGS. 16A and 16b depict printed part 1601, part outline 1602 and detected defects 1603.

FIG. 17A is a pictorial diagram showing an image of a 3D printedspecimen 1701 viewed with standard room light illuminated. FIG. 17B is apictorial diagram showing an example of a birefringence image of thespecimen 1701 or part being printed shown in FIG. 17A, obtained using anapparatus similar to that depicted in FIG. 14 . Here two crosspolarizers are used, one placed in front of the source, and anotherplaced in front of the camera, and illumination with white light. Colorsred 1702, yellow 1703, green 1704, and blue 1705 indicate variations inbirefringence due to different stresses in the printed material.

It should be obvious to those skilled in the art that the birefringenceimage obtained similar to that shown in FIG. 17B will show birefringenceand indicate stress either at the top surface, namely the surface thatis being printed, or stress induced on the already printed portion ofthe specimen as it is being printed, or both.

FIG. 18A is a pictorial diagram showing images and data illustrating anexample of images and data obtained using modulated speckle illuminationas described in the present invention. Bright spots in the imageindicate presence of voids and line breakage. FIG. 18B is a pictorialdiagram showing an image of a 3D printed specimen viewed by microscopeinspection, showing a pit (indicated by the arrow) that results in abright spot in the image shown in FIG. 18B. FIGS. 18A and 18B depictpart outline 1801, detected defects 1802, details of print lines 1803,and a void 1804 viewed under a microscope in FIG. 18B.

In some embodiments, modulated speckle illumination detection describedherein enables detection of voids, line breakage, surface roughnessvariations, and deviation of the printed surface from the desiredsurface.

Using multi-parameter detection enables a robust real-time inspectionmethod that ensures printed part quality. It provides measurementredundancy, maximizing likelihood of detecting defects that mayotherwise be missed using a single parameter sensing approach, andavoids false readings. In some embodiments, the apparatus depicted inFIGS. 3 to 14 are used for quality control and used as an add-on unitfor quality control and feedback to additive manufacturing (AM) toolavailable in the market.

The apparatus described in this application is an AM chamber-mountedarchitecture as shown in FIG. 3 , with the optics designed to enabledetection within the movement range of the AM unit manufactured part.

In other embodiments, the apparatus can be an attachment to the AM unit.

Yet in another embodiment, the apparatus depicted in FIGS. 3 to 14 canbe made to view the printed sample through a chamber window.

In another embodiment similar to FIG. 3 , the apparatus described inFIGS. 1 to 14 can be used as a stand-alone unit for post fabricationinspection of the print-head mounted architecture.

In other embodiments, the light delivery, the cameras, or both can becoupled via fiber optics, a fiber array, or fiber bundles or combinationthereof, to make the apparatus compact.

The advantage of the use of multi-parameter approach is that eachparameter reveals various types of defects, thus it covers a broad rangeof print quality issues in a compact, light-weight, and high sensitivityrobust manner.

Using the angular scanning imaging approach, defects are revealed in afield deposition model (FDM) printed plastic part that contained somedefects, such as gaps between the lines. Illumination with sourcesplaced at two different radial angles, one at 160 degrees and another at170 degrees, where 0 degrees is referred to the camera view, differentdefects are revealed, as shown in FIG. 15A and FIG. 15B, where thebright lines indicate the gap between the print layers. Here, light isreflected from the print lines of the layer below the top surface. Tomake the data machine ready for automatic testing, a series of digitalprocessing steps are performed to remove the background, and the resultsof the digitally processed images for 160 and 170 degree illuminationare shown in FIG. 15C and FIG. 15D, respectively. The data from thesetwo figures are digitally combined, namely integrated, and the result isshown in FIG. 15E, revealing the multiple lines with missing gapsindicated by the arrows. As a comparison, microscopic inspection of thepart after being printed shows where these defects are, as shown in FIG.15F. This example illustrates detection of small gaps in print linesusing the angular or radial scanning illumination without the need forhigh-magnification inspection using a microscope.

In some embodiment the angular scans depicted in FIG. 2 and FIG. 3reveals incorrect print angles or print angle variations. An example ofdetection of incorrect print angle is depicted in FIGS. 19A to 19C. Inthis example, the incident angles are at 90 and 30 degrees radialillumination as shown in FIG. 19A and FIG. 19B. After performingdifferential computation and digital filtering, a defect, namely printareas that are at different angles than the remaining surface arerevealed, as shown inside the dotted circle in FIG. 19C. FIGS. 19A to19C depict part outline 1901, and detected defects 1902.

Print Quality Assessment by Polarization Imaging

Polarization measurements can distinguish between different types ofsurface finish or surface angle, and reveal deviation from a desiredprint surface. Parallel and perpendicular polarized light have differentreflectivity from a dielectric surface, and this difference depends onthe angle of incidence. Using two polarization states will reveal adifference in surface finish and changes in angle of print, particularlywhen the two states are subtracted. Two polarization states measurementscan be achieved by several methods, such as:

-   -   a. using rotating polarizers in front of a camera as depicted in        FIG. 12 ;    -   b. using two cameras next to each other with polarizers placed        in front of them at vertical and horizontal orientation;    -   c. using a beam sputter and polarizer as shown in FIG. 13A;    -   d. using a polarization beam splitter directing light to two        different cameras as shown in FIG. 13B;    -   e. using a lens array and polarizers as shown in FIGS. 13C, 13D,        13E; or    -   f. using a fine pitch polarizer array as depicted in FIG. 13F.

Polarization-based defect detection is demonstrated using 3D printedspecimens, as shown in FIGS. 16A and 16B. FIG. 16A is a photograph ofthe specimen with standard room lighting. FIG. 16B is a polarizationimage taken using a vertically oriented polarizer in front of thecamera. At this angle, surface reflection from the specimen issuppressed by the vertical polarizer, because reflection is primarilyparallel polarized to the surface. However, a section indicated by thetwo dots in FIG. 16B, the image clearly indicates incorrect print angleand therefore has much higher reflectivity since polarized reflection isdependent on the angle of incidence.

Polarization Based Birefringence and Stress Measurements:

Another application of polarization-based detection is assessing printedpart stress on optically clear materials by measuring birefringence,namely:

$\begin{matrix}{{\Delta\varphi} = {\left( \frac{2\pi\; d}{\lambda_{0}} \right)\left( {{n_{0} - n_{e}}} \right)}} & \left( {{Eq}.\mspace{14mu} 3} \right)\end{matrix}$

where λ_(o) is the wavelength in vacuum, d is the optical path length,and n_(e) and n_(o) refer to refractive indexes of e- and o-waves.Stress build up in the material can be measured using two crosspolarizers, one in front of the source, and another in front of thecamera. If a monochromatic light is used, such as a narrow-band LED,then fringes appear that indicate stress buildup. Closely positionedfringes indicate high stress. From such measurements, birefringence canbe calculated using Jones matrix formulation.

Another approach to birefringence measurement is to use a broad-spectrumlight source, such as white light illumination, and use a color camera,with cross polarizers, as described above. In this case, color fringesindicate stress. An example of birefringence measurement using a clearplastic printed part is shown in FIGS. 17A and 17B.

Detection of Defects and Modulated Speckle Illumination

Speckle noise is often a nuisance in coherent imaging applications. Inthe application however, coherent illumination is utilized by to detectvery small variations in print lines, such as voids and pits. Because ofits coherence characteristics, laser illumination results in specklepattern when it passes through a diffuse media. Speckle size dependentson the random distribution of the diffuse media, and aperture size orthe illumination spot incident on the diffuse media. When this diffuseillumination pattern is incident on a print surface with areas thatcontain pits, voids, or small defects on the order of the speckle size,very bright signal is detected by the camera viewing the illuminatedpart. Therefore, small defects can be detected by this approach. Anothermethod of generating a speckle illumination is using a multi-mode fiber.The two methods of generating speckle pattern are shown in FIGS. 7A to7D.

The observed image however will be very noisy, which is a characteristicof coherent illumination. To reduce speckle noise from the image whilemaintaining the advantage of coherent detection, either the randommedia, or the multi-mode fiber shown in FIGS. 7A to 7D are moved tosmooth the detected image¹.

To ensure that the signal is due to pits or other small defects, and tominimize chance of false calling a defect, the speckle generation sourceis spatially modulated as shown in FIGS. 7A to 7D. Dust and othersources of noise can cause bright spot in the image as well. Pits andother stationary defects result in a bright spot in the image whichre-appear as the speckle generation source is moved, or spatiallymodulated, whereas random speckle noise is a one-time occurrence.Therefore, spatial modulation will enable elimination of false readings.This approach can easily distinguish between signal due to actualdefects in the print and due to dust and other particles, because thesignal from defects is relatively stationary with respect to the sample.

Bright spots are observed as shown in FIG. 18A indicating detecteddefects 1802. Inspection of the part with a microscope, reveals smallpits or a void 1804 shown in FIG. 18B.

Detection of such defects can be essential for applications wheremaintaining uniform line width is crucial. For example, in applicationswhere deposited layers have specific conductivity, printed electronics,then a pit or a void 1804 as shown in FIG. 18B can result in reductionin conductivity of the line, and therefore diminished performance.

Multi-Wavelength Imaging

Multi-wavelength imaging is utilized for two reasons. First, for in-situmonitoring multi-material prints, and second, for birefringencemeasurements when combined with polarization imaging. Second,multi-wavelength imaging is used for monitoring stress buildup inoptically clear materials. Multi-wavelength measurements are achievedusing multi-color LED-s combined with monochrome cameras, or using whitelight sources combined with color cameras as depicted in FIGS. 9 and 14.

For the apparatus depicted in various figures in the present invention,the camera image is digitized, transferred to a computer and imageprocessing and computing are conventionally performed.

In some embodiments similar to FIGS. 7A to 7D, the coherent source, is alaser diode, a super luminescent source, a light emitting diode (LED), alight source or an LED with a narrow band wavelength filter placed infront of it or in the optical path, a gas laser, a solid state laser, orany other coherent or partially coherent source.

In another embodiment similar to FIGS. 7A to 7D, multiple coherent orpartially coherent light sources of the same or different wavelengthsare used to enable testing of materials of different characteristics andreflectivity.

Yet in other embodiments similar to FIG. 7C, speckle size is fixed,varied, or controlled to detect various size defects by controlling theillumination spot size on the diffuse media, or by selection of diffusemedia granularity, or a combination thereof.

Yet in other embodiments similar to FIG. 7D, speckle size is fixed,varied, or controlled to detect various size defects by controllingoptical fiber shape, size of the granularity, or polishing grit off thetip, the tapering angle, or a combination thereof.

Coherent illumination will generate an image that is full of specklenoise which makes it difficult to separate the signal from the defectivearea from noise. To overcome this, the present invention employs specklenoise reduction technique using a rapidly moving diffuser. Note thateven though the speckle pattern is moving, it will still reveal thedefects, but noise in the image will be significantly reduced.

In some embodiments similar to FIGS. 3 to 14 , the obtained data andimages are digitally processed using digital filter, digitalcorrelation, convolution, Fourier filtering and Fourier analysis,Fourier transforms, differentiation, image addition, subtraction,multiplication, linear algebra and matrix calculations, morphologicalprocessing, neural computing, wavelet transforms, thresholding andcalibration, such as background removal. These digital processes areperformed either on each camera image, or on more camera images, orcombining all camera images, performing spatial processing such as inbetween pixels, in a single image, between various images, or temporalcompetition and analysis, such as between different frames, or acombination thereof.

In other embodiments similar to FIGS. 3 to 14 and data obtained similarto. FIGS. 15E, 16B, 17B, and 18A, the image may contain defectinformation, as well as edge and other features due to specimen shapeand print that is not a defect. In this case, digital processingdescribed above is performed to distinguish between defective andnon-defect signature. It should be obvious to those skilled in the artthat an image from defect map and image from standard images orcombining various imaging apparatus described herein enables distinctionbetween defect and non-light signature using various digital processingtechniques described above.

Assignment of a Digital Defect Value

In an embodiment similar to FIGS. 2, 3, 4, and 7 to 19 and other figuresdepicted herein, data/defect map obtained similar to those shown inFIGS. 4, 6, 15E, 16B, 17B, and 18A, and other figures herein, the defectmap is converted to a digital value by threshold and/or summing thedetected defect areas. For example, in an image data such as shown inFIGS. 4A, 4B and 15E, first defect data is separated from other featuresdue to specimen shape, and the summing the pixel values which results indefect value.

Using Feedback for Real-Time Correction

In other embodiments similar to various FIGS. 2 to 19 , the detectedimages and data are used to locate defects and deviation from theexpected print layer, and feedback is used to correct or compensate forthese defects. Example of correction includes filling voids, lines,print other features in the next print layers to compensate for missinglines. If a bulging occurs, next layer prints around the bulging area.If a defect is determined to be too severe, or if the cumulative defectvalues reach a prescribed threshold value, the print is stopped to avoidwasting material. The severity of the defects is calculated by using aprescribed threshold either on individual sensor camera and apparatus,and various methods described in the present invention, or on acombination of one or more of them.

Various Embodiments and Various Applications of the Sensor

In some embodiments similar to FIGS. 2, 5A to 5C, 7, and 10 , amonochromatic light, a laser, a white light, a broad spectral light witha spectral filter in front of it, a spectral are used. In otherembodiments a filter in front of the camera, or a color camera, or acombination thereof are used.

In some embodiments, speckle illumination detection described hereinenables detection of voids, line breakage, surface roughness variations,and deviation of the printed surface from the desired surface.

The apparatus described in this application is an AM chamber-mountedarchitecture as shown in FIG. 2 , with the optics designed to enabledetection within the movement range of the AM unit manufactured part.

In other embodiments, the apparatus can be an attachment to the AM unit.

Yet in another embodiment, the apparatus depicted herein can be made toview the printed sample through a chamber window.

In another embodiment similar to FIG. 2 , the apparatus is used as astand-alone unit for post fabrication inspection of the print-headmounted architecture.

In other embodiments, the light delivery, the cameras, or both can becoupled via fiber optics, a fiber array, or fiber bundles or combinationthereof, to make the apparatus compact.

In some embodiments similar to FIGS. 2, 4, 7, and 10 , the obtained dataand images are digitally processed using digital filter, digitalcorrelation, convolution, Fourier filtering and Fourier analysis,Fourier transforms, differentiation, image addition, subtraction,multiplication, linear algebra and matrix calculations, morphologicalprocessing, neural computing, wavelet transforms, thresholding andcalibration, such as background removal. These digital processes areperformed either on each camera image, or on more camera images, orcombining all camera images, performing spatial processing such as inbetween pixels, in a single image, between various images, or temporalcompetition and analysis, such as between different frames, or acombination thereof.

In other embodiments similar to FIGS. 2, 4, 7, and 10 and data obtainedsimilar to FIGS. 4, 6, and 8 , the image may contain defect information,as well as edge and other features due to specimen shape and print thatis not a defect. In this case, digital processing described above isperformed to distinguish between defective and non-defect signature. Itshould be obvious to those skilled in the art that an image from defectmap and image from standard images or combining various imagingapparatus described herein enables distinction between defect andnon-light signature using various digital processing techniquesdescribed herein.

In various embodiments, several architectures can be configured toproduce polarization measurements, and birefringence measurements usingvarious alternative embodiments using one or more of the followingcombination of components as depicted in various FIGS. 3, 9, 12, and 13.

In some embodiments similar to FIGS. 5, 9, 12, 13A to 13F, and 14 , amulti-wavelength and polarization measurements are combined.

In other embodiments similar to FIGS. 5, 9, 12, 13A to 13F, and 14 , acamera with multi-wavelength channel outputs are used to producemulti-color images.

In other embodiments similar to FIGS. 5, 9, 12, 13A to 13F, and 14 , acamera with multi-wavelength such as red, green, blue and infrared (IR)channel outputs are used to produce multi-spectral images.

In other embodiments similar to FIGS. 5, 9, 12, 13A to 13F, and 14 , amonochrome light, such as a halogen lamp with filter, light emittingdiode (LED) or a laser used as a light source.

In other embodiments similar to FIGS. 5, 9, 12, 13A to 13F, and 14 , amulti-wavelength variable or tunable wavelength is used as a lightsource.

In other embodiments similar to FIGS. 12, 13A to 13F, and 14 , an inputpolarizer is used for controlling incident light polarization.

In other embodiments similar to FIGS. 12, 13A to 13F, and 14 , an inputpolarizer followed by a wave-plate is used for controlling incidentlight polarization.

In other embodiments similar to FIGS. 12, 13A to 13F, and 14 , apolarizer in front of the camera.

In other embodiments similar to FIGS. 12, 13A to 13F, and 14 , acombination of input polarizer and polarizer in front of the camera.

In other embodiments similar to FIGS. 12, 13A to 13F, and 14 , acombination of input polarizer and a wave-plate, and polarizer in frontof the camera.

In other embodiments similar to FIGS. 12, 13A to 13F, and 14 , apolarization beam splitter is used in front of the cameras.

In other embodiments similar to FIGS. 5, 9, 12, 13A to 13F, and 14 , anarray of sources are used for illumination.

In alternative embodiments, sensor arrangements described throughoutthis patent application and depicted in FIGS. 3 to 14 , are used forin-space manufacturing.

In alternative embodiments, sensor arrangements described throughoutthis patent application and depicted in FIGS. 1-14 , are added to ormade part of a fused deposition modeling (FDM) machine.

In alternative embodiments, sensor arrangements described throughout anddepicted in FIGS. 1-14 , are used for detecting and characterizingvoids, inclusions, line breakage, sag, bulging, filament slump, andvariations in surface finish, missing lines, and variations in linespacing.

In alternative embodiments, sensor arrangements described throughoutthis patent application and depicted in FIGS. 1-14 , are used forplastic part manufacturing.

In alternative embodiments, sensor arrangements described throughoutthis patent application and depicted in FIGS. 1-14 , are used for metalpart manufacturing.

In alternative embodiments, sensor arrangements described throughoutthis patent application and depicted in FIGS. 1-14 , are used for nylonpart manufacturing.

In alternative embodiments, sensor arrangements described throughoutthis patent application and depicted in FIGS. 1-14 , are used fororganic, inorganic, or metallic part manufacturing.

In alternative embodiments, sensor arrangements described throughoutthis patent application and depicted in FIGS. 1-14 , are used in astereolithography (SLA) equipment, Polyjet, direct laser melting andsintering, powder bed laser melting or sintering, electron beam meltingsintering or powder bed electron beam melting or sintering, powder bedmelting and sintering, multi-jet fusion (MJF), selective laser sintering(SLS), direct metal laser sintering (DMLS), direct metal laser melting(DMLS), or any other laser melting equipment, either as an add on unit,or as a diagnostic unit for post process inspection.

In alternative embodiments, sensor arrangements described throughoutthis patent application and depicted in FIGS. 1-14 , are used inacoustic or ultrasonic melting and sintering equipment, either as an addon unit, or as a diagnostic unit for post process inspection.

In alternative embodiments, sensor arrangements described throughoutthis patent application and depicted in FIGS. 1-14 , are used incomputer numerical control (CNC) machining equipment, either as an addon unit, or as a diagnostic unit for post process inspection.

In alternative embodiments, sensor arrangements described throughoutthis patent application and depicted in FIGS. 1-14 , are used inadditive manufacturing equipment, either as an add on unit, or as adiagnostic unit for post process inspection.

In alternative embodiments, sensor arrangements described throughoutthis patent application and depicted in FIGS. 1-14 , are used insubtractive manufacturing equipment, either as an add on unit, or as adiagnostic unit for post process inspection.

In other embodiments similar to FIGS. 2, 5, 7, 9 and 10 , a camera withmulti-wavelength channel outputs are used to produce multi-color images.

In other embodiments similar to FIGS. 2, 5, 7, 9 and 10 , a camera withmulti-wavelength such as red, green, blue and infrared (IR) channeloutputs are used to produce multi-spectral images.

In other embodiments similar to FIGS. 2, 5, 7, 9 and 10 , a monochromelight, such as a halogen lamp with filter, light emitting diode (LED) ora laser used as a light source.

In other embodiments similar to FIGS. 2, 5, 7, 9 and 10 , amulti-wavelength variable or tunable wavelength is used as a lightsource.

In other embodiments similar to FIGS. 2, 5, 7, 9 and 10 , an array ofsources is used for illumination.

In alternative embodiments, sensor arrangements described throughout anddepicted in FIGS. 2, 5, 7, 9 and 10 , are used for manufacturing qualityassessment.

In alternative embodiments, sensor arrangements described throughout anddepicted in FIGS. 2, 5, 7, 9 and 10 , are added to or made part of adirect metal laser sintering (DMLS) machine.

In alternative embodiments, sensor arrangements described throughout anddepicted in FIGS. 2, 5, 7, 9 and 10 , are added to or made part of alaser melting machine.

In alternative embodiments, sensor arrangements described throughout anddepicted in FIGS. 2, 5, 7, 9 and 10 , are added to or made part of anadditive metal manufacturing machine.

In alternative embodiments, sensor arrangements described throughout anddepicted in FIGS. 2, 5, 7, 9 and 10 , are used for detecting andcharacterizing voids, inclusions, line breakage, sag, bulging, andvariations in surface finish, missing lines, and variations in linespacing.

In alternative embodiments, sensor arrangements described throughout anddepicted in FIGS. 2, 5, 7, 9 and 10 , are used for metal, plastic,ceramic, glass, and circuit board manufacturing.

In alternative embodiments, sensor arrangements described throughout anddepicted in FIGS. 2, 5, 7, 9 and 10 , are used for metal partmanufacturing.

In alternative embodiments, sensor arrangements described throughout anddepicted in FIGS. 2, 5, 7, 9 and 10 , are used for nylon partmanufacturing.

In alternative embodiments, sensor arrangements described throughout anddepicted in FIGS. 2, 5, 7, 9 and 10 , are used for organic, inorganic,or metallic part manufacturing.

In alternative embodiments, sensor arrangements described and depictedin FIGS. 2, 5, 7, 9 and 10 , are used in a stereo-lithography (SLA)equipment, Polyjet, direct laser melting and sintering, powder bed lasermelting or sintering, electron beam melting sintering or powder bedelectron beam melting or sintering, powder bed melting and sintering,multi-jet fusion (MJF), selective laser sintering (SLS), direct metallaser sintering (DMLS), direct metal laser melting (DMLS), or any otherlaser melting equipment, either as an add on unit, or as a diagnosticunit for post process inspection.

In alternative embodiments, sensor arrangements described throughout anddepicted in FIGS. 2, 5, 7, 9 and 10 , are used in acoustic or ultrasonicmelting and sintering equipment, either as an add on unit, or as adiagnostic unit for post process inspection.

In alternative embodiments, sensor arrangements described throughout anddepicted in FIGS. 2, 5, 7, 9 and 10 , are used in computer numericalcontrol (CNC) machining equipment, either as an add on unit, or as adiagnostic unit for post process inspection.

In alternative embodiments, sensor arrangements described throughout anddepicted in FIGS. 2, 5, 7, 9 and 10 , are used in additive manufacturingequipment, either as an add on unit, or as a diagnostic unit for postprocess inspection.

In alternative embodiments, sensor arrangements described throughout anddepicted in FIGS. 2, 5, 7, 9 and 10 , are used in subtractivemanufacturing equipment, either as an add on unit, or as a diagnosticunit for post process inspection, or both.

In alternative embodiments, sensor arrangements described throughout anddepicted in FIGS. 2, 5, 7, 9 and 10 , the outputs of each sensingapproach or sensor is used independently and combined with other sensingapproaches or sensors described herein to produce final result of defectmap.

In alternative embodiments, sensor arrangements described throughout anddepicted in FIGS. 2, 5, 7, 9 and 10 , the outputs of each sensingapproach or sensor is combined or compared with one or more anothersensing approach or sensor to produce a correlated result. In someembodiments this is achieved by subtraction, addition, multiplication,correlation or convolution, digital shifting, Fourier analysis andtransforms, linear algebra and matrix calculations.

In alternative embodiments, sensor arrangements described throughout anddepicted in FIGS. 2, 5, 7, 9 and 10 the outputs of each sensor isadjusted and corrected for movement of the part if the print bed moves,is raised or lowered, and if the part moves. This is achieved bytransferring movement data from the 3D printer to the sensor unit andusing a calibration data to correct for changes in image width, size andany image distortion.

The preceding merely illustrates the principles of the invention. Itwill thus be appreciated that those skilled in the art will be able todevise various arrangements which, although not explicitly described orshown herein, embody the principles of the invention and are includedwithin its spirit and scope. Furthermore, all examples and conditionallanguage recited herein are principally intended expressly to be onlyfor pedagogical purposes and to aid the reader in understanding theprinciples of the invention and the concepts contributed by theinventors to furthering the art, and are to be construed as beingwithout limitation to such specifically recited examples and conditions.Moreover, all statements herein reciting principles, aspects, andembodiments of the invention, as well as specific examples thereof, areintended to encompass both structural and functional equivalentsthereof. Additionally, it is intended that such equivalents include bothcurrently known equivalents and equivalents developed in the future,i.e., any elements developed that perform the same function, regardlessof structure.

This description of the exemplary embodiments is intended to be read inconnection with the figures of the accompanying drawing, which are to beconsidered part of the entire written description. In the description,relative terms such as “lower,” “upper,” “horizontal,” “vertical,”“above,” “below,” “up,” “down,” “top” and “bottom” as well asderivatives thereof (e.g., “horizontally,” “downwardly,” “upwardly,”etc.) should be construed to refer to the orientation as then describedor as shown in the drawing under discussion. These relative terms arefor convenience of description and do not require that the apparatus beconstructed or operated in a particular orientation. Terms concerningattachments, coupling and the like, such as “connected” and“interconnected,” refer to a relationship wherein structures are securedor attached to one another either directly or indirectly throughintervening structures, as well as both movable or rigid attachments orrelationships, unless expressly described otherwise.

All patents, publications, scientific articles, web sites, and otherdocuments and materials referenced or mentioned herein are indicative ofthe levels of skill of those skilled in the art to which the inventionpertains, and each such referenced document and material is herebyincorporated by reference to the same extent as if it had beenincorporated by reference in its entirety individually or set forthherein in its entirety.

The applicant reserves the right to physically incorporate into thisspecification any and all materials and information from any suchpatents, publications, scientific articles, web sites, electronicallyavailable information, and other referenced materials or documents tothe extent such incorporated materials and information are notinconsistent with the description herein.

The written description portion of this patent includes all claims.Furthermore, all claims, including all original claims as well as allclaims from any and all priority documents, are hereby incorporated byreference in their entirety into the written description portion of thespecification, and Applicant(s) reserve the right to physicallyincorporate into the written description or any other portion of theapplication, any and all such claims. Thus, for example, under nocircumstances may the patent be interpreted as allegedly not providing awritten description for a claim on the assertion that the precisewording of the claim is not set forth in haec verba in writtendescription portion of the patent.

The claims will be interpreted according to law. However, andnotwithstanding the alleged or perceived ease or difficulty ofinterpreting any claim or portion thereof, under no circumstances mayany adjustment or amendment of a claim or any portion thereof duringprosecution of the application or applications leading to this patent beinterpreted as having forfeited any right to any and all equivalentsthereof that do not form a part of the prior art.

All of the features disclosed in this specification may be combined inany combination. Thus, unless expressly stated otherwise, each featuredisclosed is only an example of a generic series of equivalent orsimilar features.

It is to be understood that while the invention has been described inconjunction with the detailed description thereof, the foregoingdescription is intended to illustrate and not limit the scope of theinvention, which is defined by the scope of the appended claims. Thus,from the foregoing, it will be appreciated that, although specificembodiments of the invention have been described herein for the purposeof illustration, various modifications may be made without deviatingfrom the spirit and scope of the invention. Other aspects, advantages,and modifications are within the scope of the following claims and thepresent invention is not limited except as by the appended claims.

The specific methods and compositions described herein arerepresentative of preferred embodiments and are exemplary and notintended as limitations on the scope of the invention. Other objects,aspects, and embodiments will occur to those skilled in the art uponconsideration of this specification, and are encompassed within thespirit of the invention as defined by the scope of the claims. It willbe readily apparent to one skilled in the art that varying substitutionsand modifications may be made to the invention disclosed herein withoutdeparting from the scope and spirit of the invention. The inventionillustratively described herein suitably may be practiced in the absenceof any element or elements, or limitation or limitations, which is notspecifically disclosed herein as essential. Thus, for example, in eachinstance herein, in embodiments or examples of the present invention,the terms “comprising”, “including”, “containing”, etc. are to be readexpansively and without limitation. The methods and processesillustratively described herein suitably may be practiced in differingorders of steps, and that they are not necessarily restricted to theorders of steps indicated herein or in the claims.

The terms and expressions that have been employed are used as terms ofdescription and not of limitation, and there is no intent in the use ofsuch terms and expressions to exclude any equivalent of the featuresshown and described or portions thereof, but it is recognized thatvarious modifications are possible within the scope of the invention asclaimed. Thus, it will be understood that although the present inventionhas been specifically disclosed by various embodiments and/or preferredembodiments and optional features, any and all modifications andvariations of the concepts herein disclosed that may be resorted to bythose skilled in the art are considered to be within the scope of thisinvention as defined by the appended claims.

The invention has been described broadly and generically herein. Each ofthe narrower species and sub-generic groupings falling within thegeneric disclosure also form part of the invention. This includes thegeneric description of the invention with a proviso or negativelimitation removing any subject matter from the genus, regardless ofwhether or not the excised material is specifically recited herein.

It is also to be understood that as used herein and in the appendedclaims, the singular forms “a,” “an,” and “the” include plural referenceunless the context clearly dictates otherwise, the term “X and/or Y”means “X” or “Y” or both “X” and “Y”, and the letter “s” following anoun designates both the plural and singular forms of that noun. Inaddition, where features or aspects of the invention are described interms of Markush groups, it is intended and those skilled in the artwill recognize, that the invention embraces and is also therebydescribed in terms of any individual member or subgroup of members ofthe Markush group.

Other embodiments are within the following claims. Therefore, the patentmay not be interpreted to be limited to the specific examples orembodiments or methods specifically and/or expressly disclosed herein.Under no circumstances may the patent be interpreted to be limited byany statement made by any Examiner or any other official or employee ofthe Patent and Trademark Office unless such statement is specificallyand without qualification or reservation expressly adopted in aresponsive writing by Applicants.

Although the invention has been described in terms of exemplaryembodiments, it is not limited thereto. Rather, the appended claimsshould be construed broadly, to include other variants and embodimentsof the invention, which may be made by those skilled in the art withoutdeparting from the scope and range of equivalents of the invention.

Other modifications and implementations will occur to those skilled inthe art without departing from the spirit and the scope of the inventionas claimed. Accordingly, the description hereinabove is not intended tolimit the invention, except as indicated in the appended claims.

What is claimed is:
 1. A method of constructing a multi-modal inspection apparatus for detecting defects in an additive manufactured part during printing, comprising: providing an additive manufacturing device having a printhead for manufacturing an additive manufactured part, wherein the additive manufacturing device includes a laser entrance window; providing a speckle generation source located adjacent to the window; providing a plurality of light sources located adjacent to the speckle generation source; providing a plurality of image capturing located at a pre-determined distance away from the speckle generation source and the plurality of light sources, wherein the speckle generation source, the plurality of light sources, and the plurality of image capturing devices are used to inspect the additive manufactured part as the additive manufactured part is being made by the additive manufacturing device, to provide feedback to the additive manufacturing device for correction of the manufacturing of the additive manufactured part by the additive manufacturing device, or to stop the manufacturing of the additive manufactured part, and wherein the plurality of image capturing devices further includes a polarization image detector for use in providing information about variations in a finish of the printed surface and measuring stress in the additive manufactured part as the additive manufactured is being made by the additive manufacturing device, wherein the polarization image detector includes; a beam splitter, a plurality of polarizers located adjacent to the beam splitter, and a plurality of cameras, where each camera of the plurality of cameras is located adjacent a polarizer of the plurality of polarizers; and providing a processor operatively connected to the plurality of image capturing devices for processing information from the plurality of image capturing devices and providing a map of any defects in the additive manufactured part.
 2. A sensing device, comprising: an additive manufacturing device having a printhead for manufacturing an additive manufactured part, wherein the additive manufacturing device includes a laser entrance window; a speckle generation source located adjacent to the window; a plurality of light sources located adjacent to the speckle generation source; a plurality of image capturing devices located at a pre-determined distance away from the speckle generation source and the plurality of light sources, wherein the speckle generation source, the plurality of light sources, and the plurality of image capturing devices are used to inspect the additive manufactured part as the additive manufactured part is being made by the additive manufacturing device, to provide feedback to the additive manufacturing device for correction of the manufacturing of the additive manufactured part by the additive manufacturing device, or to stop the manufacturing of the additive manufactured part, and wherein the plurality of image capturing devices further includes a polarization image detector for use in providing information about variations in a finish of the printed surface and measuring stress in the additive manufactured part as the additive manufactured is being made by the additive manufacturing device, wherein the polarization image detector includes; a beam splitter, a plurality of polarizers located adjacent to the beam splitter, and a plurality of cameras, wherein each camera of the plurality of cameras is located adjacent a polarizer of the plurality of polarizers; and a processor operatively connected to the plurality of image capturing devices for processing information from the plurality of image capturing devices and providing a map of any defects in the additive manufactured part. 